"8 Major Maintenance Misconceptions for Excavators: Have You Fallen into Any of Them?!"

The engine oil is only added and not changed

Many drivers pay attention to checking the oil level of the lubricating oil and adding it according to the standard, but they neglect to inspect the quality of the lubricating oil and replace the deteriorated oil. As a result, some moving parts of the engine always operate in a poor lubrication environment, thereby accelerating the wear of each part

2. Misuse and random application of butter

Butter is a commonly used lubricating grease in the repair of construction machinery, which can play a role in lubrication and sealing. Therefore, some mechanics will apply a layer of grease on the cylinder gasket when installing it, believing that this can enhance the sealing performance of the diesel engine. Little do they know that doing so actually affects the working performance of the diesel engine.

When disassembling and assembling the cylinder gasket, special attention should be paid to its sealing quality. If grease is applied to the cylinder gasket during installation, when the cylinder head bolts are tightened, some of the grease will be squeezed into the water and oil channels of the cylinder. The grease remaining between the cylinder gaskets, due to the influence of high temperature during cylinder operation, will partly flow into the cylinder and burn, while the other part will remain on the mating surface between the cylinder block and the cylinder head, creating a gap between the cylinder gasket, the cylinder head and the plane of the engine block High-temperature and high-pressure gas can easily impact the cylinder gasket from here, damaging it and causing gas leakage.

3. Do not check the plunger stroke allowance

When maintaining and debugging the fuel injection pump, the first step is to check this stroke allowance to determine whether the fuel injection pump is still allowed to be adjusted.

When inspecting, the following different methods should be adopted according to the different structures of the fuel injection pump:

a) Rotate the camshaft, push the plunger to the top dead center, then remove the oil outlet valve and valve seat, and measure with a depth gauge.

b) After the plunger is pushed to the top dead center, use a screwdriver to lift the spring seat of the plunger spring to raise the plunger to the highest point. Then, insert a thickness gauge between the lower plane of the plunger and the tappet adjustment bolt to measure. The standard stroke allowance of the plunger is approximately 1.5mm, and the ultimate stroke allowance after wear should be no less than 0.5mm.

4. Polish the bearing bush with sandpaper

Some people, when replacing bearing shells, use sandpaper to grind them instead of scraping the shells in order to increase the contact area between the bearing shells and the crankshaft. This method is highly unadvisable in actual maintenance because the abrasive grains on the sandpaper are relatively hard, while the alloy of the bearing bush is relatively soft. As a result, during grinding, the abrasive grains can easily embed into the alloy, which will accelerate the wear of the journal when the diesel engine is working and shorten the service life of the crankshaft.

5. The new cylinder liners and pistons can be installed without selection

When replacing cylinder liners and pistons, people may think that the new cylinder liners and pistons are all standard parts and interchangeable, and can be used immediately after installation. In fact, both the cylinder liner and the piston have a certain tolerance range for their dimensions. If the largest-sized cylinder liner is matched with the smaller-sized piston, the fit clearance will be too large, resulting in weak compression and difficult starting.

Therefore, when changing the cylinder liner and piston, it is necessary to check the size group codes of the standard cylinder liner and piston. The size group codes of the standard piston and the standard cylinder liner used must be the same. Only in this way can the standard fit clearance between the two be guaranteed.

6. The bolts are tightened too much

During the disassembly and assembly of construction machinery, many parts of the bolts have specified torque requirements, such as the transmission box, cylinder head, wheel hub, connecting rod and front axle, etc. The tightening torque is specifically stipulated in the manual and must not be changed at will. However, many users mistakenly believe that tightening it tighter will be safer. But tightening it too much can cause the screws or bolts to break, and it may also lead to malfunctions due to thread slippage.

7. Inaccurate measurement of cylinder clearance

When measuring the cylinder clearance, it was not measured in the direction perpendicular to the piston pin hole at the piston skirt, but in other directions. The structural feature of the aluminum alloy piston is that it is smaller at the top and larger at the bottom, forming a cone. Moreover, the cross-section of the skirt is elliptical, so the cylinder clearance along the circumferential direction is not equal.

When measuring, it is stipulated that the gap in the direction of the major axis of the ellipse should be taken as the standard, that is, the gap between the piston skirt and the direction perpendicular to the piston pin hole should be measured. This measurement method is more convenient and accurate. Moreover, during the reciprocating motion, the direction of the piston skirt perpendicular to the piston pin hole wears out more due to the lateral pressure.

8. The piston is heated by an open flame

Since the piston and the piston pin are in an interference fit, when installing the piston pin, the piston should be heated and expanded first. At this time, some maintenance personnel will directly heat the piston over an open flame, which is a very wrong practice.

If the piston cools down naturally after reaching a certain temperature, its metallographic structure will be damaged and its wear resistance will be greatly reduced, and its service life will also be significantly shortened. When installing the piston pin, place the piston in hot oil and heat it evenly to make it expand slowly. Do not heat it directly with an open flame.